JP5183357B2 - Inkjet recording head - Google Patents

Description

  The present invention relates to an ink jet recording head including a plurality of ejection openings for ejecting yellow ink, magenta ink, and cyan ink.

  In recent years, with the widespread use of personal computers, word processors, facsimiles, and the like in offices and homes, recording apparatuses of various recording systems have been provided as information output devices for these devices. Among them, it is relatively easy for a recording apparatus such as an ink jet printer to have a color recording specification using a plurality of types of ink. In addition, there are various advantages such as low noise during operation, high-quality printing on a wide variety of print media, and further miniaturization. From such a point, this ink jet recording apparatus is suitable for personal use in offices and homes. Among the ink jet recording apparatuses, a serial type recording apparatus that performs recording while a recording head reciprocates with respect to a recording medium is widely used because it can record high-quality images at low cost.

  In a serial type recording apparatus, when a recording head capable of discharging a plurality of colors of ink is mounted on a carriage and bidirectional recording is performed to record an image when the carriage moves in both forward and backward directions, The ink ejection order (ejection order) is reversed between the forward path and the backward path. Due to the difference in the order of placing the inks of the respective colors, band-shaped density unevenness (hereinafter also referred to as “bidirectional color difference”) may occur on the recorded image. Therefore, various proposals have been made in the past to reduce such bidirectional color difference.

  For example, in the recording head described in Patent Document 1, among the five ejection port arrays, one is the ejection port array for yellow ink, two is the ejection port array for cyan ink, and the other two Is an ejection port array for magenta ink. The yellow ink ejection port array is located at the center of the five ejection port arrays, one cyan ink ejection port and one magenta ink ejection port array are located on the left side, and the right side is the cyan ink ejection line. One ejection port array for magenta ink is positioned one by one. The discharge port arrays for cyan ink and magenta ink are positioned symmetrically about the discharge port array for yellow ink, so that the discharge order of the inks of the respective colors is the same during forward and backward recording. Can be used properly.

  In such a recording head, the yellow ink ejection port array is provided with only ejection ports for ejecting large ink droplets, and each of the ejection port arrays for cyan ink and magenta ink has large ink. A discharge port for discharging a droplet and a small ink droplet is provided. The reason is that for yellow ink with high lightness, the graininess on the image is not noticeable even if there are no small ink droplets, while for cyan ink and magenta ink with low lightness, if the ink droplets are not small ink droplets, This is because the graininess is easily noticeable. Small yellow ink droplets are not necessary to reduce graininess. For this reason, yellow ink is provided with only a discharge port for large ink droplets.

JP 2004-001491 A

  In recent years, further improvement in recording speed has been demanded, and a method for reducing the number of scans (the number of scans) is known as a method for meeting the demand. If it is desired to record at the same density, the ink ejection density per scan is increased by reducing the number of scans.

  In Patent Document 1, the discharge port array for yellow ink has discharge ports for discharging large ink droplets arranged on both sides of one ink supply port. Each of the magenta ink and cyan ink ejection port arrays has ejection ports for ejecting large ink droplets on either side of one ink supply port, and ejects smaller ink droplets on the other side. Are arranged. For this reason, large magenta and cyan ink droplets are ejected from ejection ports located on either side of the ink supply port, while large yellow ink droplets are ejected from ejection ports located on both sides of the ink supply port. It will be. Therefore, large yellow ink droplets have a high discharge density per unit area of the recording head, and when recording a high-density image, a strong air flow accompanying ink discharge is generated in the vicinity of the yellow ink discharge port array. To do. When a secondary color image is recorded by the ink droplets ejected from the ejection port row for yellow ink and the ejection port row for magenta ink or cyan ink adjacent to the ejection port row for yellow ink, color unevenness may occur. That is, the landing position of the ink droplets ejected from the latter ejection port array is disturbed by the air flow generated in the vicinity of the former ejection port array, and there is a possibility that color unevenness occurs. Such color unevenness is referred to as “airflow unevenness”. In particular, small ink droplets are more strongly affected by airflow.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an ink jet recording head capable of minimizing the influence of an air flow generated when ink is ejected from a small number of ejection port arrays while reducing the size of the recording head.

The inkjet recording head of the present invention is an inkjet recording head in which a plurality of ejection openings for ejecting yellow ink, magenta ink, and cyan ink are formed, and one of the yellow ink, magenta ink, and cyan ink is used. The plurality of discharge ports for discharging are positioned along the first discharge port row, and the plurality of discharge ports for discharging one of the remaining two are positioned along the second discharge port row The plurality of discharge ports for discharging the remaining one are positioned along a third discharge port row, and the first, second, and third discharge port rows are along a predetermined direction. The first discharge port arrays formed in parallel, wherein the number of the first discharge port arrays is smaller than the number of the second and third discharge port arrays, and are adjacent to each other in the predetermined direction; Said second or third Between the outlet and columns, the yellow ink, positioned along different fourth ink plurality of ejection ports fourth ejection opening arrays for ejecting the magenta ink, and cyan ink, the fourth The ink is a gray ink .

  According to the present invention, a small number of first ejection port arrays that eject one of the three primary colors of cyan, magenta, and yellow, and a large number of second and third ejections that eject the other two. Between the outlet row, a fourth discharge port row for discharging a fourth ink different from those inks is located. As a result, when ink is ejected from the first ejection port array at a high density, the influence of the airflow generated along with it on the ink ejected from the second and third ejection port arrays can be reduced. . As a result, color unevenness can be reduced and high-quality images can be recorded. In addition, since the influence of the airflow can be suppressed to a small value without specially increasing the adjacent interval between the plurality of ejection port arrays, the recording head can be reduced in size.

  Regarding the fourth ink, whatever color ink it is, it can be replaced by inks of the three primary colors cyan, magenta, and yellow. For example, when the ink is ejected from the first ejection port array at a predetermined density or higher, the fourth ink can be replaced with three colors of cyan, magenta, and yellow. Further, the fourth ink can be used when the discharge density of the ink discharged from the first discharge port array is a low density lower than a predetermined value. As a result, when ejecting ink from the first ejection port array at high density, it is possible to avoid “air flow unevenness” that occurs in the ink ejected from the ejection ports adjacent to the first ejection port array. Further, the use of the fourth ink can further improve the image recording quality. Further, since the cyan, magenta, and yellow inks are the three primary colors, the first and fourth ejection port arrays are drawn when drawing a mixed color of the ink ejected from the first and fourth ejection port arrays. Can also be used at a discharge density that does not cause “air flow unevenness”.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
FIG. 16 is a perspective view for explaining an example of the ink jet recording head.

  The ink jet recording head 1 of this example includes an ink supply unit 2 and an ink discharge unit 3. The ink supply unit 2 includes a holding body 2 </ b> A that holds an ink tank (not shown) for supplying ink, and is connected to the ink discharge port 3 so as to supply ink to the ink discharge unit 3. Has been. The ink ejection unit 3 includes a chip (Bk chip) 10 for ejecting a black pigment ink and a chip (color chip) 20 for ejecting a plurality of dye color inks.

  FIG. 1 is a schematic configuration diagram of the color chip 20, in which a plurality of common liquid chambers 21 connected to the ink supply unit 2 are formed. The common liquid chamber 21 has a rectangular shape. Discharge port arrays L in which a plurality of discharge ports 22 and 23 are arranged are formed on both sides of each common liquid chamber 21. The discharge ports 22 and 23 open to a nozzle plate connected to a member that forms the common liquid chamber 21 (common liquid chamber forming member). In the common liquid chamber forming member, an electrothermal conversion element (heater) is disposed at a position facing the discharge ports 22 and 23.

  A nozzle (a nozzle) is formed by a heater, a foaming chamber surrounding the heater, discharge ports 22 and 23 opened on the surface of the foaming chamber facing the heater, and an ink flow path connecting the foaming chamber and the common liquid chamber 21. Inkjet nozzle) is configured.

  In each of the discharge port arrays L, 264 discharge ports 22 and 23 are arranged at an interval of 600 dpi (about 42.3 um). Further, the discharge ports 22 and 23 are arranged in a staggered manner in the discharge port arrays L on both sides of the common liquid chamber 21, and a total of 528 nozzles are arranged at intervals of 1200 dpi (about 21.2 um) in the discharge port arrays L on both sides. It is arranged. A total of 528 discharge ports 22 and 23 in the discharge port array L on both sides of the common liquid chamber 21 form a discharge port array group LG. In FIG. 1, six discharge ports 22 and 23 are formed in one discharge port row L for convenience of explanation.

  In the present embodiment, eight common liquid chambers 21 are formed, and eight discharge port array groups LG are also formed. For the eight common liquid chambers 21, in order from the left in FIG. 1, black ink (Bk), cyan ink (C), magenta ink (M), gray ink (G), yellow ink (Y), gray Ink (G), magenta ink (M), and cyan ink (C) are supplied. There is one discharge port array group LG for black ink (Bk) and yellow ink (Y). There are two discharge port array groups LG for cyan ink (C), magenta ink (M), and gray ink (G), and these discharge port array groups LG are common liquid chambers for yellow ink (Y). It is located symmetrically about 21.

  FIG. 2A is an explanatory diagram of the ejection port array group LG (Bk, Y) for black ink (Bk) and yellow ink (Y). The ejection port 22 for ejecting black ink and yellow ink has a diameter of about 16 μm and ejects about 5 pl of ink droplets (large ink droplets). 24 is an electrothermal conversion element (heater), 25 is a foaming chamber surrounding the heater 24, and 26 is an ink flow path connecting the foaming chamber 25 and the common liquid chamber 21. Reference numeral 27 denotes a column (foreign matter inhibition column) that prevents foreign matter in the ink from entering the ink flow path 26.

  FIG. 2B is an explanatory diagram of the ejection port array group LG (C, M, G) for cyan ink (C), magenta ink (M), and gray ink (G). When located on the left and right of the common liquid chamber 21, the discharge ports 22 arranged on one side of the discharge port array L have a diameter of about 16 μm, like the discharge ports 22 for discharging black ink and yellow ink. , About 5 pl of ink droplets (large ink droplets) are ejected. The ejection ports 23 arranged in the other ejection port array L have a diameter of about 12 μm and eject about 2 pl of ink droplets (small ink droplets). In these discharge port array groups LG (C, M, G), large discharge ports 22 are arranged in the discharge port array L located on the far side from the yellow ink (Y) discharge port array group LG (Y). Has been. On the other hand, small discharge ports 23 are arranged in the discharge port array L located on the side closer to the discharge port array group LG (Y) for yellow ink (Y).

A total of two ejection port array groups LG (G) for gray ink (G) are provided on the left and right sides of the ejection port array group LG (Y) for yellow ink (Y). It is located symmetrically with LG (Y) as the center. Such two discharge port array groups LG (G) are provided for the following purposes.
(1) Smoothing gradation change from highlight to middle when recording monochrome photographs.
(2) To smooth the gradation change in the gray color portion during color tone photo recording.
(3) When recording on plain paper, it is used for recording the gray portion.

Further, the discharge port array group LG (Bk) for black ink (Bk) is not symmetrical about the discharge port array group LG (Y) of yellow ink (Y) for the following purposes. Only one is provided.
(1) High-density monochrome is recorded when recording monochrome photographs.
(2) Ink is used when recording color photographs.

  In the present embodiment, the dye black ink (Bk) discharged from the color chip 20 is not used for recording on plain paper. For recording on plain paper, black pigment ink ejected from the Bk chip is used.

Next, the ink ejection operation in the inkjet recording head 1 will be described.
A drive current is selectively supplied to the heaters 24 of the respective nozzles in accordance with an electric signal given from a drive unit (not shown) to the ink discharge unit 3. By energizing the heater 24, the ink near the heater generates heat and boils. Ink is discharged from the discharge ports 22 and 23 facing the heater 24 using the pressure generated by the boiling. When all the heaters 24 to be energized are energized simultaneously, the voltage drop becomes large. Therefore, in the present embodiment, the 264 heaters 24 arranged on the discharge port array L are divided into 16 groups as the same groups as those located every 16th. One set includes 16 heaters 24. The 16 sets of heaters 24 are time-division driven (16-time division), thereby suppressing a voltage drop. The driving cycle for one heater 24 is 15 kHz.
16 x 16 (time division) = 256

  Thus, the number of heaters 24 is 256 instead of the actual number of arrangements 264. This is because there are eight (= 264-256) dummy heaters that are not used for recording. The dummy heater is used to discharge the mixed color ink at the end of the common liquid chamber 21 from the discharge port when color mixing occurs in the ink in the common liquid chamber 21.

  Next, a printer (inkjet recording apparatus) using the inkjet recording head 1 of the present embodiment will be described.

  The printer of this example is a so-called multi-function printer in which a scanner 4 is incorporated as shown in FIG. FIG. 3 is a perspective view when the upper cover of the multifunction printer is lifted.

  The printer includes a carriage 5 that reciprocates in the main scanning direction indicated by an arrow X, and the recording head 1 is mounted on the carriage 5. The recording head 1 records an image on a sheet (recording medium) by ejecting ink while moving with the carriage 5 in an arrow X direction (in this example, a direction orthogonal to the ejection port array) intersecting the ejection port array L. (Recording scan) The paper is fed from the paper feed tray of the printer and fed in the sub-scanning direction that intersects (in the present example, orthogonal) to the main scanning direction of the arrow X. A scanner 4 for capturing a recorded image is provided at the top of the printer. The scanner 4 is integrated with the upper cover of the printer.

Next, the recording operation will be described.
Image reading data from the scanner 4 is received by the buffer unit of the scanner 4, and image processing is performed on the data in the buffer unit by the scanner image processing unit. The image-processed data is sent to the print buffer unit and then received by the recording image processing unit, and paper is fed from the paper feed tray.

  A recording signal corresponding to the image is sent to the recording head 1 via the wiring of the carriage 5 for one scan, and the recording head 1 moves along with the carriage 5 in the forward direction (arrow X1 direction) accordingly. Discharge (outward scan). Thereafter, the paper is sent in the sub-scanning direction by 128 dots at 600 dpi. Thereafter, the recording signal corresponding to the image is sent to the recording head 1 through the wiring of the carriage 5 for one scan, and the recording head 1 moves in the backward direction (arrow X2 direction) together with the carriage 5 accordingly. Ink is ejected (return scan). In the ejection port array L, 256 ejection ports 22 and 23 are arranged at intervals corresponding to 600 dpi, and therefore 128 of them are on the raster on which ink is ejected by the previous forward scanning. Ink is ejected. Thereafter, the paper is sent in the sub-scanning direction by 128 dots at 600 dpi.

  By repeating such scanning (forward scanning, backward scanning) and conveyance of the sheet, recording for one page of the sheet is performed. In this example, a so-called two-pass printing method is employed in which one raster is completed by two scans. Therefore, the recording image processing unit divides recording data for one scan into two scans using a mask.

(Magenta gradient drawing)
Next, a magenta gradation drawing method will be described with reference to FIG. It is assumed that the gradation reaches a sufficiently high density when two large dots formed by large ink droplets and two small dots formed by small ink droplets are formed per 600 dpi.

  First, the discharge of small ink droplets of magenta ink is started, and the discharge ratio (small dot formation ratio) in the unit recording area is gradually increased as the density increases. Then, after the ejection ratio of the small ink droplets reaches a certain ratio, large ink droplets of magenta ink begin to be ejected as the density increases. This is to reduce the graininess of the image. When only a large magenta ink droplet lands on the recording surface, the graininess of the image deteriorates because the diameter of the ink droplet is large. However, when the large ink droplet is landed after the small ink droplet is sufficiently landed, the dot of the large ink droplet is mixed into the dot of the small ink droplet and becomes inconspicuous.

  Thereafter, as the density increases, the large ink droplet ejection ratio (large dot formation ratio) is gradually increased. When the discharge ratio of small ink droplets to large ink droplets becomes 1: 1, a sufficiently high density is reached.

  In this example, a two-pass recording method is adopted. Therefore, for the darkest portion of such gradation, large ink that forms one large dot on average from the two ejection port array groups LG (M) in each of the forward scanning and the backward scanning. A droplet and a small ink droplet forming one small dot are ejected. Since the two ejection port array groups LG (M) are formed with a sufficient interval therebetween, no airflow unevenness occurs at the time of magenta drawing regardless of the recording density, and the image quality is good.

(Drawing gradation that changes from yellow to red)
Next, a gradation drawing method for changing from a yellow color to a red color will be described with reference to FIG. It is assumed that yellow at this time has a sufficiently high density, and three dots are formed with yellow ink per 600 dpi. The red gradation has a sufficiently high density per 600 dpi when two dots by large ink droplets of magenta ink, two dots by small ink droplets of magenta ink, and three dots by yellow ink are formed. It is assumed that

The color is changed from yellow to red as follows.
The red color is a color in which yellow ink and magenta ink are mixed in a one-to-one relationship. Therefore, the yellow ink is always ejected so that three dots of yellow ink are formed by two scans per 600 dpi until the yellow color changes to the red color.

  When the color changes from yellow to red, a small ink droplet of magenta ink starts to be ejected, and the ejection ratio (dot formation ratio) is gradually increased. Then, when the discharge ratio of the small ink droplets reaches a certain ratio, the large ink droplets of magenta ink are started to be discharged. Thereafter, the ejection ratio of the large ink droplet of magenta ink is gradually increased, and when the ejection ratio of the small ink droplet and the large ink droplet of magenta ink becomes 1: 1, a sufficiently dark red color is obtained.

  In this example, a two-pass recording method is adopted. Therefore, for the portion where the red color is the darkest, the large magenta ink that forms one large dot on average from the two ejection port array groups LG (M) in each of the forward scanning and the backward scanning. A droplet and a small magenta ink droplet forming one small dot are ejected. For the darkest portion of the red color, yellow large ink that forms 1.5 dots on average from one ejection port array group LG (Y) in each of the forward scan and the backward scan. Drops are ejected. The ejection port array group LG (M) for magenta ink and the ejection port array group LG (Y) for yellow ink are not adjacent to each other, and they are formed with a sufficient interval. For this reason, when drawing a color that changes from yellow to red, there is no airflow unevenness regardless of the recording density, and the image quality is improved.

(Drawing gradation that changes from cyan to blue)
Next, a gradation drawing method for changing from cyan to blue will be described with reference to FIG. It is assumed that the cyan color at this time has a sufficiently high density, and two large dots formed by large cyan ink droplets and two small dots formed by small cyan ink droplets are formed per 600 dpi. In 600 dpi, the blue gradation formed 2 dots with large magenta ink droplets, 2 dots with small ink droplets, 2 dots with large cyan ink droplets, and 2 dots with the small ink droplets. Sometimes a sufficiently high concentration is reached.

The color is changed from cyan to blue as follows.
The blue color is a color in which cyan ink and magenta ink are mixed approximately one to one. Therefore, the cyan ink always scans two large dots of cyan large ink droplets and two small dots of cyan small ink droplets per 600 dpi until the color changes from cyan to blue. The cyan ink is ejected so as to form in the above.

  When the color changes from cyan to blue, magenta small ink droplets begin to be ejected, and the ejection ratio is gradually increased. Then, when the ejection ratio of the small magenta ink droplets reaches a certain ratio, the ejection of the large magenta ink droplets is started. After that, when the ejection ratio of magenta large ink droplets is gradually increased and the ejection ratio of small magenta ink droplets to large ink droplets becomes 1: 1, a sufficiently dark blue color is obtained.

  In this example, a two-pass recording method is adopted. For this reason, in the portion where the blue color is the darkest, the large magenta ink that forms one large dot on average from the two ejection port array groups LG (M) in each of the forward scanning and the backward scanning. A droplet and a small magenta ink droplet forming one small dot are ejected. For the darkest part of the blue color, cyan large ink that forms one large dot from the two ejection port array groups LG (C) on average in each of the forward scanning and the backward scanning. A droplet and a small cyan ink droplet forming one small dot are ejected. The ejection port array group LG (M) for magenta ink and the ejection port array group LG (C) for cyan ink are adjacent to each other, and the distance between them is small. However, on average, 0.5 dots of large ink droplets and 0.5 dots of small ink droplets are formed for each of the ejection port array groups LG (M) and LG (C). The ink ejection density in these ejection port array groups is sufficiently small. Therefore, the landing position is not disturbed in any small ink droplets of cyan ink and magenta ink. Therefore, when drawing a color that changes from cyan to blue, airflow non-uniformity does not occur regardless of the recording density, and the image quality is improved.

(Drawing gradation that changes from yellow to black)
Next, a gradation drawing method for changing from a yellow color to a black color will be described with reference to FIG. At this time, the yellow color and the black color have sufficiently high densities, and the number of dots formed is as shown in FIG.

The yellow color is changed to the black color as follows.
Since the black color has the same hue as the color in which yellow ink, magenta ink, and cyan ink are mixed in equal amounts, the yellow ink gradually decreases the ejection ratio until it changes from yellow to black. To go. The magenta and cyan small ink droplets are ejected from the state where the yellow ink is ejected so that 3 dots per 600 dpi are formed by two scans using only the yellow ink, and the ratio is gradually increased. Accordingly, the yellow ink ejection ratio is gradually reduced. When the discharge ratio of yellow ink reaches the ratio of forming one dot with an average large ink droplet per 600 dpi, the gray small ink droplet starts to be discharged, and the discharge ratio is gradually increased.

  The gray ink is an ink having a density obtained by mixing cyan ink, yellow ink, and magenta ink in equal amounts and diluting to 1/4.

  Therefore, one dot by the small gray ink droplet is replaced with 0.25 dot by the small magenta ink droplet, 0.25 dot by the small cyan ink droplet, and 0.125 dot by the yellow ink droplet. Can do. However, in order to reach the black color, it is necessary to increase the discharge ratio of magenta ink and cyan ink, so the replacement ratio of magenta ink and cyan ink is subtracted, but the discharge ratio of magenta ink and cyan ink becomes moderate. All of these discharge ratios increase.

  As in the case of the magenta ink in the red color described above, when the ejection ratio of the small gray ink droplets reaches a certain ratio, the shift is made to the ejection of the large gray ink droplets. In the meantime, the discharge ratio of yellow ink decreases, and the discharge ratio of magenta ink and cyan ink gradually increases.

  When the ejection ratio of large ink droplets of gray ink reaches a certain ratio, the black ink starts to be ejected. Accordingly, the ratio of yellow, magenta, cyan, and gray inks decreases. Then, when the black ink discharge ratio reaches a ratio of forming 3 dots per 600 dpi in 2 scans, the discharge of other inks is stopped. At this time, the color is black.

  In this example, a two-pass recording method is adopted. Therefore, on the portion where the yellow color is darkest, large yellow ink droplets forming 1.5 dots on average from the ejection port array group LG (Y) in each of the forward scan and the backward scan. Discharged. On the other hand, for the portion where the black color is the darkest, on the forward and backward scans, on average, large black ink droplets forming 1.5 dots are formed from the ejection port array group LG (Bk). Discharged. When a small gray ink droplet starts to be ejected, the yellow ink ejection port array group LG (Y) adjacent to the gray ink ejection port array group LG (G) is subjected to the forward scanning and the backward scanning. On average, ink droplets forming one dot are ejected. Further, the magenta ink ejection port array group LG (M) ejects, on average, small ink droplets that form 0.25 dots in each of the forward scan and the backward scan. These discharge port array groups LG (Y), LG (G), and LG (M) are adjacent to each other, and their interval is small. However, as in the case of blue drawing, the ejection density of ink in these ejection port arrays is sufficiently small, so that the landing positions of the ink droplets ejected therefrom are not disturbed.

  Further, the distance (distance between the ejection port arrays) between the black ink ejection port array group LG (Bk) and the adjacent cyan ink ejection port array group LG (C) is small. For this reason, small cyan ink droplets are affected by the impact of airflow. However, since the density of the black color is sufficiently high, the image quality is not affected. In this example, since the maximum density of black color was achieved using only black ink, small cyan ink droplets were affected by airflow (airflow unevenness). However, mixing cyan, magenta, yellow, and gray inks with black and black and setting the ink parameters to achieve the highest density of black will prevent the effects of airflow in small cyan droplets. It becomes possible.

  In any case, the image quality is good regardless of the recording density even when drawing a gradation that changes from yellow to black.

(Comparative example)
Next, as a comparative example, as shown in FIG. 8, in order from the left, black (Bk), gray (G), cyan (C), magenta (M), yellow (Y), magenta (M), cyan (C) A recording head having a configuration in which ejection port arrays for gray (G) ink are arranged will be described.

  Consider a case where a gradation changing from yellow to red is drawn using the recording head of this comparative example.

  While yellow ink is being ejected so as to form 3 dots per 600 dpi in 2 scans, magenta small ink droplets begin to be ejected in the same manner as in the above-described embodiment. In this comparative example, the discharge port array group LG (Y) for yellow ink and the two discharge port array groups LG (M) for magenta ink are adjacent to each other (the distance between them) The distance is short. For this reason, the landing position of the magenta small ink droplets may be disturbed by the airflow when the yellow ink droplets are ejected. Therefore, when drawing a gradation that changes from yellow to red, uneven airflow may occur, and image quality may deteriorate.

  Next, a case where a gradation changing from yellow to black is drawn using the recording head of this comparative example will be considered.

  The color is changed from yellow to black as follows. That is, from the yellow ink ejection state in which 3 dots per 600 dpi are formed in 2 scans using only yellow ink, the ejection of the small gray ink droplets is gradually increased. After that, as in the case of the above-described embodiment, as the gray ink discharge ratio is increased, the yellow ink discharge ratio is decreased, and when the gray ink discharge ratio reaches a certain ratio, black ink is discharged. To do.

  In this comparative example, the discharge port array group LG (Y) for yellow ink and the discharge port array group LG (G) for gray ink are not adjacent to each other, and therefore the distance between them is long. The distance between the black ink ejection port array group LG (Bk) and the gray ink ejection port array group LG (G) adjacent thereto is short. For this reason, although the small gray ink droplets are affected by the airflow, the density of the black color is sufficiently high, and the image quality is not affected. Therefore, when drawing a gradation that changes from yellow to black, the image quality is good regardless of the recording density.

(Comparison between this embodiment and comparative example)
In this embodiment, since the image quality can be improved at the time of drawing of any gradation that changes from yellow to red and gradation that changes from yellow to black, the advantage of this embodiment is clear. .

  Other ways to avoid uneven airflow include simply increasing the distance between the ejection port arrays, lowering the ink ejection density, slowing the carriage movement speed, and increasing the size of the ejected ink droplets. Can be considered. However, when the distance between the ejection port arrays is simply increased, the size of the recording head increases, which increases the cost of the recording head. Further, when the discharge density is lowered or the carriage moving speed is lowered, the recording speed is lowered. Further, when the size of the ejected ink droplet is increased, the granularity of the recorded image is increased, and the image quality is deteriorated. Compared with these airflow non-uniformity avoiding means, the superiority of this embodiment is clear.

(Second Embodiment)
In the embodiment described above, the gray ink ejection port array group LG (G) is positioned between the magenta ink and yellow ink ejection port array groups LG (M) and LG (Y). However, instead of the ejection port array group LG (G), the ejection port array group LG (Bk) for black ink may be positioned.

  In this case, the black ink ejection port array group LG (Bk) adjacent to the cyan ink ejection port array group LG (C) may be changed to another ink ejection port array group. Good. Alternatively, as shown in FIG. 9, the discharge port row group LG (Bk) itself may be eliminated, and the common liquid chamber 21 and the discharge port row group LG may be set to seven.

  As shown in FIG. 9, two large black ink droplets and small ink droplets can be ejected by arranging the two black ink ejection port array groups LG (Bk) symmetrically. When recording on plain paper, the black ink can be used. Further, by ejecting large black ink droplets and small ink droplets, gray tone expression is improved as compared to the case where there are no black small ink droplets.

  Further, when a gradation changing from yellow to black is drawn using the recording head of FIG. 9, the ejection start timing of the black small ink droplet is the ejection start timing of the gray small ink droplet in FIG. It becomes closer to black than. In this case as well, the image quality is better than when only cyan, magenta, and yellow inks are used.

(Third embodiment)
In addition, as shown in FIG. 10, the ejection port array group LG (R) for red ink (R) is arranged between the ejection port array groups LG (M) and LG (Y) for magenta ink and yellow ink. May be.

  By setting the red ink to a color with higher saturation than that obtained by mixing the magenta ink and the yellow ink, it is possible to depict the image with high saturation in an image such as a sunset with a strong red hue. Green ink or blue ink may be used instead of red ink. Similarly, by setting these inks to a color with a higher saturation than that obtained by mixing two inks, it is possible to depict images with high saturation when recording an image with a strong hue. Even in such a configuration, when a lot of yellow ink is used, the use of cyan ink and magenta ink instead of red ink, green ink, or blue ink eliminates the occurrence of airflow unevenness, and image quality. Becomes better.

  Further, a light cyan ink discharge port array group may be arranged between the magenta ink and yellow ink discharge port array groups LG (M) and LG (Y). The light cyan is an ink in which the density of the cyan dye is lowered by increasing the solvent component of the cyan ink. By using such light cyan, the gradation from the cyan highlight portion to the intermediate portion becomes smooth. Even in such a configuration, when the discharge density of yellow ink is high, the use of cyan ink without using light cyan eliminates the occurrence of airflow unevenness and improves image quality. When light magenta is used instead of light cyan, the gradation from the magenta highlight portion to the middle portion is similarly smooth.

  In the present embodiment, the cyan ink ejection row group LG (C) is positioned outside the yellow ink ejection port row group LG (Y) with respect to the magenta ink ejection row group LG (M). . However, the two ejection port array groups LG (C) and the two ejection port array groups LG (M) may be interchanged.

(Fourth embodiment)
In the present embodiment described above, two types of large and small discharge ports 22 and 23 are formed as discharge ports for discharging cyan, magenta, and gray inks. However, the types of discharge ports are not limited to two.

  For example, as shown in FIG. 11, there are three large, medium, and small for each of the ejection port arrays LG (C), LG (M), and LG (G) for cyan ink, magenta ink, and gray ink. You may provide the discharge port 22,23,24 which discharges the ink drop of a kind of size.

  In these discharge port array groups LG (C), LG (M), and LG (G), as shown in FIG. 11 and FIG. On the side close to the outlet row group LG (Y), the discharge ports 23 and the discharge ports 24 are arranged in a staggered manner at an interval of 1200 dpi. The ejection port 23 for ejecting medium ink droplets has an elliptical shape with a minor axis of about 10 μm and a major axis of about 12 μm, and the ejection port 24 for ejecting small ink droplets has a circular shape of about 9 μm. . Large ink drops have a volume of about 5 pl, medium ink drops have a volume of about 2 pl, and small ink drops have a volume of about 1 pl.

  On the other hand, the discharge port array groups LG (Y) and LG (Bk) for yellow ink and black ink are formed in the same manner as in the above-described embodiment. That is, as shown in FIG. 11 and FIG. 12A, in these discharge port array groups, the discharge ports 22 are formed on the discharge port array L at intervals of 600 dpi, and the diameter is about 16 μm. , Eject large ink droplets.

  Since the ejection port array groups LG (C), LG (M), and LG (G) eject ink droplets of three types of large, medium, and small sizes, gradation expression is roughly divided into three stages. That is, it is possible to start using medium ink droplets when the discharge ratio of small ink droplets becomes a constant ratio, and then start using large ink droplets when the discharge ratio of medium ink droplets reaches a constant ratio. .

  Even in the case of this embodiment, the image quality is good as in the above-described embodiment. For example, when drawing a gradation that changes from a yellow color to a black color, the image quality is improved by using a gray ink after the discharge density of the yellow ink is sufficiently lowered, as in the above-described embodiment. It becomes.

  This embodiment is excellent in the following points. That is, since there are three types of dot sizes, gradation expression is good in the frequently used gradation of each color gamut, and high density black color recording is possible. Furthermore, by using gray ink as an intermediate tone expression color, the number of ejection port array groups can be reduced to 8 and the size of the ink ejection unit 3 (see FIG. 16) can be reduced.

  Since there are three types of dot sizes, when light cyan ink and light magenta ink are also used, their use density area is covered with normal density cyan ink and magenta ink. If only one type of halftone expression ink can be used, the gray ink is prioritized. However, if there is no limitation on the size of the ink ejection unit 3, the image quality is better when the light cyan ink and the light magenta ink are also used.

(Fifth embodiment)
FIG. 13 is a diagram for explaining the configuration of a recording head according to the fifth embodiment of the present invention. Eight common liquid chambers 21 are formed, and eight ejection port array groups LG are also formed. . In the eight common liquid chambers 21, in order from the left in FIG. 13, black ink (Bk), cyan ink (C), magenta ink (M), red ink (R), yellow ink (Y), green ink ( Gr), magenta ink (M), and cyan ink (C) are supplied. There is one ejection port array LG for black ink (Bk), yellow ink (Y), red ink (R), and green ink (Gr). There are two discharge port array groups LG of cyan ink (C) and magenta ink (M), and these discharge port array groups LG are symmetrical about the common liquid chamber 21 for yellow ink (Y). Is located.

  In the ejection port array groups LG (Bk), LG (Y), LG (R), LG (Gr) for black ink (Bk), yellow ink (Y), red ink (R), and green ink (Gr) The discharge ports 22 are arranged at intervals of 600 dpi on both sides of the common liquid chamber 21. The diameter of the ejection port 22 is about 16 μm, and a large ink droplet of about 5 pl is ejected.

  On the other hand, the discharge port array group LG (C), LG (M) for cyan ink (C) and magenta ink (M) has a discharge port 22 with a diameter of about 16 μm for discharging a large ink droplet of about 5 pl, and about A discharge port 23 having a diameter of about 12 μm for discharging a 2 pl small ink droplet is formed. That is, in these discharge port array groups LG (C) and LG (M), the discharge ports 22 are formed at intervals of 600 dpi on both sides of the common liquid chamber 21 and on the side close to the discharge port array group LG (Y). The discharge ports 23 are formed at intervals of 600 dpi on the side far from the discharge port array group LG (Y).

  The red ink is prepared by selecting a color material having a higher saturation than that obtained by mixing the magenta ink and the yellow ink. Similarly, the green ink is prepared by selecting a color material having a higher saturation than that obtained by mixing the cyan ink and the yellow ink. Red ink and green ink are used to enable recording of high saturation when recording vivid colors such as sunsets and grasslands.

(Drawing gradation that changes from yellow to red)
Next, a gradation drawing method for changing from yellow to red will be described with reference to FIG. It is assumed that the yellow color at this time has a sufficiently high density, and three large dots are formed by large yellow ink droplets per 600 dpi. The red gradation is assumed to reach a sufficiently high density when three large dots are formed by large red ink droplets per 600 dpi. The red ink has a higher saturation, but the yellow ink and the magenta ink are mixed in a one-to-one relationship. Therefore, each time one large red ink dot is added, the yellow ink and the magenta ink are equivalent to a large dot. The discharge ratio decreases by 0.5 dots.

The color is changed from yellow to red as follows.
In the case of this example, since the two-pass printing method is employed, the yellow color forms three large dots with large yellow ink droplets per 600 dpi in two scans. From this state, magenta small ink droplets are started to be discharged, and the discharge ratio is gradually increased. When the ejection ratio of the small magenta ink droplets reaches a certain ratio, ejection of the large magenta ink droplets is started. Thereafter, large red ink droplets are started to be discharged, and the discharge ratio is gradually increased. As the red ink is used, the amount of yellow ink and magenta ink used is gradually reduced. Then, when three large dots are formed by large red ink droplets per 600 dpi, a sufficient red color is reached.

  In the case of this example, such gradation is recorded in two passes. For this reason, in the portion where the red color is the darkest, on the forward scan and the return scan, on average, one large red dot that forms 1.5 large dots from one ejection port array group LG (R). Ink droplets are ejected. At the start of ejection of red ink droplets, yellow large ink droplets that form 1.5 large dots are ejected from the ejection port array group LG (Y) per scan. At this time, a large magenta ink droplet that forms approximately 0.25 large dots and a small magenta ink droplet that forms approximately 0.5 small dots are ejected.

  The magenta ink ejection port array group LG (M), the red ink ejection port array group LG (R), and the yellow ink ejection port array group LG (Y) on the right side in FIG. 13 are adjacent to each other. And their spacing is small. Further, as shown in FIG. 14, although the discharge density of magenta ink is low, the discharge density of yellow ink is high.

  However, since the red ink droplets are large, the ink droplets are not affected by the airflow associated with the yellow ink ejection. Therefore, when drawing a color that changes from yellow to red, airflow non-uniformity does not occur regardless of the recording density, and image quality is improved.

(Drawing gradation that changes from yellow to green)
Drawing a gradation changing from yellow to green is the same as drawing a gradation changing from yellow to red except that the roles of magenta ink and cyan ink are changed.

  Also at this time, since the green ink droplets are large, the ink droplets are not affected by the airflow accompanying the discharge of the yellow ink. Therefore, even when a color changing from yellow to green is drawn, airflow non-uniformity does not occur regardless of the recording density, and the image quality is improved.

  In this embodiment, the magenta ink ejection port array group LG (M) and the yellow ink ejection port array group LG (Y), and the red ink ejection port array group LG (R), A discharge port array group LG (Gr) for green ink is located. However, one of the ejection port array groups LG (R) and LG (Gr) may be an ejection port array group for high-saturation blue ink. Also in this case, the same effect can be obtained by drawing a gradation changing from yellow to blue as in the case of drawing a gradation changing from yellow to red or green.

  Further, instead of red ink and green ink, gray ink and light gray ink may be used. In this case, the red image quality can be improved, and the gradation can be made smooth in monochrome expression.

  Further, instead of red ink and green ink, light cyan ink and light magenta ink may be used. In this case, the image quality of the red color can be improved, and the gradation can be smoothed in the halftone between cyan and magenta.

  The diameter of the discharge port 22 for red ink and green ink may be one type of 12 μm instead of one type of 16 μm. In this case, in the red color or the green color, gradation expression near magenta or cyan can be made smooth.

  In addition, a hue formed from one or more of cyan, magenta, and yellow ink between the magenta ink and yellow ink ejection port array groups LG (M) and LG (Y), and a light color Or an ejection port array group for ejecting high chroma color ink. In this case, halftone gradation can be expressed with high gradation or high saturation, and even if the discharge density of yellow ink is high, the occurrence of uneven airflow is eliminated and image quality is improved. Can do.

(Other embodiments)
In any of the embodiments, as the ink discharge method, a discharge method using the pressure of bubbles in the ink generated by the heat generated by the heater is used. However, a discharge method using a piezoelectric element or the like may be used. it can.

  In any of the embodiments, the ejection port array group LG is configured to include two or three ejection port arrays L. However, the ejection port array group LG is configured to include only one ejection port array L. May be. In such a case as well, the occurrence of airflow unevenness can be suppressed.

  In any of the embodiments, one ejection port array group is arranged between the ejection port array group LG (Y) for yellow ink and one ejection port array group LG (M) for magenta ink. did. However, as shown in FIG. 15, two or more discharge port array groups may be arranged between the discharge port array groups LG (Y) and LG (M). In FIG. 15, LG (G) is a gray ink ejection port array group, and LG (LG) is a light gray ink ejection port array group.

  The inkjet recording head of the present invention has an ejection port for ejecting yellow ink, magenta ink, and cyan ink, and an ejection port for ejecting a fourth ink different from those inks, as follows: Any configuration that includes A plurality of ejection ports for ejecting one of yellow ink, magenta ink, and cyan ink are positioned along the first ejection port array, and a plurality of ejection ports for ejecting one of the remaining two. The discharge ports are located along the second discharge port array. The plurality of discharge ports for discharging the remaining one are positioned along the third discharge port array. The first, second, and third ejection port arrays are formed in parallel along a predetermined direction, and the number of the first ejection port arrays is smaller than the number of the second and third ejection port arrays. . A plurality of ejection ports for ejecting the fourth ink are arranged between the first ejection port array and the second or third ejection port array adjacent to each other in the predetermined direction. Located along.

  Each of the first, second, third, and fourth ejection port arrays is located on both sides in a predetermined direction of the common liquid chamber to which ink is supplied, and the first, second, third, and fourth. The discharge port array group may be configured. In that case, the number of the first discharge port array groups is smaller than the number of the second discharge port array groups and the third discharge port array groups, and the first discharge port array groups adjacent to each other in the predetermined direction. A fourth outlet row group is located between the outlet row group and the second or third outlet port row group. Further, the fifth ejection port array group for ejecting the fifth ink different from the yellow ink, the magenta ink, the cyan ink, and the fourth ink may be positioned outside the third ejection port array group. Good.

  In addition, an image is recorded on a recording medium using an inkjet recording head in which the following first, second, third, and fourth ejection port arrays are formed in parallel along a predetermined direction. Can do. Each of the first, second, third, and fourth ejection port arrays has a plurality of ejection ports capable of ejecting ink, and the number of first ejection port arrays is the second and third ejection ports. Less than the number of exit lines. Further, the fourth discharge port array is located between the first discharge port array and the second or third discharge port array which are adjacent to each other in the predetermined direction. When recording an image using such a recording head, one of yellow ink, magenta ink, and cyan ink is ejected from the first ejection port array, and one of the remaining two is the first. The second ejection port array is ejected, and the remaining one is ejected from the third ejection port array. Further, a fourth ink different from the yellow ink, magenta ink, and cyan ink is ejected from the fourth ejection port array.

  Further, the present invention is not limited to the bidirectional recording type serial type recording apparatus, but can also be applied to a direction recording type recording apparatus that records an image in one of the forward path and the backward path. Furthermore, the present invention uses a long recording head that extends over the entire width direction of the recording area of the recording medium, and continuously moves the recording head and the recording medium relative to each other in one direction. The present invention can also be applied to a so-called full-line type recording apparatus that records an image on the recording medium.

It is explanatory drawing of arrangement | positioning of the discharge outlet row group in the 1st Embodiment of this invention. 1A is a schematic configuration diagram of the black ink and yellow discharge port array groups in FIG. 1, and FIG. 1B is an overview of the cyan, magenta and gray ink discharge port array groups in FIG. It is a block diagram. 1 is a perspective view of an ink jet recording apparatus to which an ink jet recording head of the present invention can be applied. FIG. 6 is an explanatory diagram of a method for drawing a magenta gradation in the first embodiment of the present invention. It is explanatory drawing of the method of drawing the gradation between yellow color and red color in the 1st Embodiment of this invention. It is explanatory drawing of the method of drawing the gradation between cyan and blue in the 1st Embodiment of this invention. It is explanatory drawing of the method of drawing the gradation between yellow color and black color in the 1st Embodiment of this invention. FIG. 4 is an explanatory diagram of a comparative example of a recording head for comparison with the first embodiment of the present invention. It is explanatory drawing of arrangement | positioning of the discharge outlet row group in the 2nd Embodiment of this invention. It is explanatory drawing of arrangement | positioning of the discharge outlet row group in the 3rd Embodiment of this invention. It is explanatory drawing of arrangement | positioning of the discharge outlet row group in the 4th Embodiment of this invention. FIG. 11A is a schematic configuration diagram of the black ink and yellow discharge port array groups in FIG. 11, and FIG. 11B is an overview of the cyan ink, magenta ink, and gray ink discharge port array groups in FIG. It is a block diagram. It is explanatory drawing of arrangement | positioning of the discharge outlet row group in the 5th Embodiment of this invention. It is explanatory drawing of the method of drawing the gradation between yellow color and red color in the 5th Embodiment of this invention. It is explanatory drawing of arrangement | positioning of the discharge outlet row group in other embodiment of this invention. 1 is a perspective view of an ink jet recording head according to a first embodiment of the present invention.

Explanation of symbols

21 Common liquid chamber 22, 22, 23 Discharge port 24 Heater 25 Foaming chamber 26 Ink flow path L Discharge port array LG Discharge port array group LG (Y) Discharge port array group for yellow ink LG (M) Discharge for magenta ink Exit line group LG (C) Cyan outlet line group LG (G) Gray ink outlet line group

Claims (5)

In an inkjet recording head having a plurality of ejection openings for ejecting yellow ink, magenta ink, and cyan ink,
The plurality of ejection ports for ejecting one of the yellow ink, magenta ink, and cyan ink are positioned along the first ejection port array, and ejecting one of the remaining two The plurality of discharge ports are positioned along the second discharge port row, and the plurality of discharge ports for discharging the remaining one are positioned along the third discharge port row,
The first, second, and third discharge port arrays are formed in parallel along a predetermined direction,
The number of the first ejection port arrays is smaller than the number of the second and third ejection port arrays,
A fourth ink different from the yellow ink, magenta ink, and cyan ink between the first ejection port array and the second or third ejection port array adjacent to each other in the predetermined direction. A plurality of outlets for discharging the liquid is located along the fourth outlet row ,
The inkjet recording head, wherein the fourth ink is a gray ink . In an inkjet recording head having a plurality of ejection openings for ejecting yellow ink, magenta ink, and cyan ink,
The plurality of ejection ports for ejecting one of the yellow ink, magenta ink, and cyan ink are positioned along the first ejection port array, and ejecting one of the remaining two The plurality of ejection ports are positioned along a second ejection port array, and the plurality of ejection ports for ejecting the remaining one are positioned along a third ejection port array, and the yellow ink, magenta A plurality of ejection openings for ejecting a fourth ink different from the ink and the cyan ink are positioned along the fourth ejection opening row;
The first, second, third, and fourth ejection port arrays are formed in parallel along a predetermined direction;
Each of the first, second, third, and fourth ejection port arrays is located on both sides in the predetermined direction of the common liquid chamber to which the ink to be ejected is supplied. And a fourth discharge port array group,
The number of the first outlet row groups is one, the number of the second and third outlet row groups is two,
The two second ejection port array groups are symmetrically positioned around the first ejection port array group in the predetermined direction, and are adjacent to the first ejection port array group,
The two third ejection port array groups are symmetrically positioned around the first ejection port array group in the predetermined direction, and are located outside the second ejection port array group,
A total of two fourth discharge port array groups are located between each of the one first discharge port array group and the two second discharge port array groups,
The fourth ink ejected from one of the two fourth ejection port array groups is a light cyan ink, and the fourth ink ejected from the other is a light magenta ink. Inkjet recording head. In an inkjet recording head having a plurality of ejection openings for ejecting yellow ink, magenta ink, and cyan ink,
The plurality of ejection ports for ejecting one of the yellow ink, magenta ink, and cyan ink are positioned along the first ejection port array, and ejecting one of the remaining two The plurality of ejection ports are positioned along a second ejection port array, and the plurality of ejection ports for ejecting the remaining one are positioned along a third ejection port array, and the yellow ink, magenta A plurality of ejection openings for ejecting a fourth ink different from the ink and the cyan ink are positioned along the fourth ejection opening row;
The first, second, third, and fourth ejection port arrays are formed in parallel along a predetermined direction;
Each of the first, second, third, and fourth ejection port arrays is located on both sides in the predetermined direction of the common liquid chamber to which the ink to be ejected is supplied. And a fourth discharge port array group,
The number of the first outlet row groups is one, the number of the second and third outlet row groups is two,
The two second ejection port array groups are symmetrically positioned around the first ejection port array group in the predetermined direction, and are adjacent to the first ejection port array group,
The two third ejection port array groups are symmetrically positioned around the first ejection port array group in the predetermined direction, and are located outside the second ejection port array group,
A total of two fourth discharge port array groups are located between each of the one first discharge port array group and the two second discharge port array groups,
The fourth ink ejected from each of the two fourth ejection port array groups is different from each other, and each of the different fourth inks is two of the yellow ink, magenta ink, and cyan ink. An ink jet recording head characterized by a hue obtained by mixing two or more . The first ink ejection orifice row ejects the ink jet recording head according to any of claims 1 3, characterized in that said yellow ink. A fifth ejection port array for ejecting a fifth ink different from the yellow ink, magenta ink, cyan ink, and the fourth ink is located outside the third ejection port array. An ink jet recording head according to any one of claims 1 to 4 .